I want to deorbit the Mun.

[Ranzear]

Exactly what it says on the tin. I want to build a craft that places a decently sized fuel tank on the leading surface of the moon with an upward pointing thruster.

My only question is: Do KSP\'s physics allow this, or is the Mun\'s trajectory fixed?

Pending an answer to that question, I might make a challenge thread for crafts capable of placing a thruster on another planetoid or satellite, such as instead an asteroid, and seeking the highest energy deliverable, then figuring how many of those craft it would take to severely disrupt the lunar orbit. ;D

[leopardenthusiast]

It\'s on rails. Sorry.

[Khrissetti]

Even if it weren\'t, the Mun has a mass of 976,000 Teratonnes travelling at 542.5 m/s have you any idea how big the thrust would need to be to deorbit something that big?

[SunJumper]

2.87X10²⁶

[Kreuzung]

And if you write a plugin to deorbit it, it goes through Kerbin and comes out at the other side ;P

[Khrissetti]

2.87X10²⁶

Is this the amount of thrust you\'d have to use? if so, what is the equation you used?

[honolululu]

0.5*mass*(velocity^2)=Kinetic Energy needed to stop an object with the same kinetic energy. Remember to square the velocity first.

Now what\'s the chemical energy in a solid booster?

All right. Just for a ballpark estimate I loaded 1 command module + 4 liquid tanks + one solid booster = 12.8 (I assume tons?)

That rocket rose to 334 meters. So at such slow speeds let\'s just forget about air resistance.

Max potential energy is rounded to mass*height*gravity=12.8*334*9.8=~42,000 tons*m^2/s^2

So it would take somewhere in the neighborhood (I hope) 6,800,000,000,000,000,000,000 solid boosters to null the velocity of the Mun.

[maltesh]

It should be noted that the amount of kinetic energy that a rocket can impart to a ship varies depending on how fast the ship is currently moving. The faster the spacecraft is moving, the more kinetic energy a burn can add to it. That\'s one of the reasons the Oberth Effect works. Conservation of energy is satisfied by the fact that the rocket engine also imparts kinetic energy to its exhaust.

As a result, the parameter you\'re looking f or here is not kinetic energy, but delta-V. If fuel mass is insignificant compared to object mass, you can get delta-V as thrust * burn time / total mass. For everythign in KSP though, fuel mass is significant, so you\'ll have to use the Tsiolkovsky Rocket Equation instead.

Also, you don\'t have to come to a dead stop at the Mun\'s orbit distance to deorbit. Because Kerbin\'s 600 km in radius, an object orbiting Kerbin at the Mun\'s distance only has to decelerate to about 175 m/s to hit Kerbin.

[Ranzear]

Actually the Mun has it\'s own radius of 200km, so for the two bodies to touch you only have to decelerate it to 236.7 m/s to get the spheres to touch, and I\'m rather fond of the \'6000mph celestial steamroller\' concept of that.

Also, my wording of \'disrupt the lunar orbit\' was rather carefully chosen, because you need only bring such an object close enough for tidal forces to start ripping it apart into interestingly destructive bits.

Naturally this idea partly came about because of a scene from The Time Machine (2002) where the moon is apparently falling out of orbit (haven\'t seen it, was in Ponies Anthology II ) and even that short clip has it breaking apart as it likely would.

So even just getting it inside of 1200km should be enough to cause some serious trouble, which is 264.6m/s at apoapsis, or just a smidge past halving the velocity.

So a change of 277m/s on an object of 9.76*10^20kg... 3.74*10^25 Joules.

I\'d consider NovaPunch parts fair game. How are we looking then?

Edit: One Petaton of TNT is 4.184E+24 Joules. It\'d take 8.94 of these to cause the disruption I prescribe, which is four hundred and forty seven million 20 Megaton warheads.

That is some serious energy.

[Khrissetti]

That was an awful, awful movie, don\'t waste your time if you\'ve not seen it.

To make that much of an impact you\'d need the explosive force of 692 billion hiroshima bombs. Pretty sure nothing in KSP even scrapes the surface of that kind of power.

[Ranzear]

Yeah, I went the nuclear equivalent route in my edit, which took a little while to recheck my math.

I\'ll believe that it\'s a horrible movie, but so too do I think the 1960 film is pretty crappy in comparison to the book, so my standard for it is gonna be rather low to start.

This idea also comes from a crazy terraforming method I devised for Venus, and man is that gonna be even crazier to think about now; short version is: You slingshot Jupiter\'s moon Europa into the inner planets and place it in orbit of Venus as a tidal driver to possibly induce core rotation and produce a magnetosphere much how Earth\'s moon is theorized to function, meanwhile you take large amounts of its ice mass and start dumping it into the atmosphere, which serves to reduce the carbon dioxide content drastically, increase atmospheric mass, and add oxygen. I suppose if you have a few million years to work on something like that the technology and energy involved is rather trivial.

[flaillomanz]

Exactly what it says on the tin. I want to build a craft that places a decently sized fuel tank on the leading surface of the moon with an upward pointing thruster.

My only question is: Do KSP\'s physics allow this, or is the Mun\'s trajectory fixed?

Pending an answer to that question, I might make a challenge thread for crafts capable of placing a thruster on another planetoid or satellite, such as instead an asteroid, and seeking the highest energy deliverable, then figuring how many of those craft it would take to severely disrupt the lunar orbit. ;D

You\'re a credit to the Mad Scientist in us all.

[Pds314]

The best way to do this would be to make a mod that allows you to do such things, and then to make another one which adds:

a 200-Trillion ton fuel tank

a gigantic rocket engine capable of burning through that at a normal Isp in a practical amount of time.

Alternatively, you could just mess with the rocket to be really massive and really high thrust (keeping a TWR of at most around 25, preferably less) then turn on infinite fuel.

Also, I am pretty sure it would be energetically cheaper to launch it into a Kerbolar Orbit or possibly even into a collision course with Eve or Duna.

Now, if we only had a way to hit the Mun with about 104 KT-impactors moving at an appropriately high speed.

[Pds314]

Oh, wait, if we hit it with Gilly at 20 km/s.... That might be enough.

Now we have to find a way to hit it with Gilly going retrograde to Kerbin's orbit.

[HoY]

Since we're talking about nuclear explosions,, and if the Mun wasn't on rails,, what do you all think about landing a few dozen Orion engines on the surface. They have Massive amounts of deltaV compared to stock combinations. And the thrust to push a small moon. I haven't used the mod personally but it's available under the Addon Development sub forum

[sporkafife]

I know it's impossible with the game's physics to deorbit any object, but I'm loving the theoretical discussion and the juicy maths detailing how crazy your ship would have to be to do it

[jwenting]

what you guys are forgetting is that you need to add the mass of the stuff you're attaching to the Mun to deorbit it to the mass you need to deorbit.

As that mass is more than the mass of the Mun itself, things get rather silly rather quick

[Synapse]

De-orbit Kerbin instead. That way we get to explore the rest of the galaxy...

[Flixxbeatz]

Scott Manley has something to say.

[bonyetty]

Mmmmm what's the DeltaV of a Kerbal jetpack? How many of the green guys would we need to send up there to bring that sucker down? And does one hemisphere of the Mun have enough area for the green guys to stand up there side by side to do the job?

[Penguinhero]

Scott Manley has a video on this

Google it

Just saying

Man addicted with polls is out CHEERS!

[HoY]

You know, something like this would actually be possible with the asteroids mod and the Orion engine mod. Rescale the 200m asteroid that has gravity to the size and mass of whichever body you like, land a crap-ton of Orion ships on our new satellite- watch the fireworks!!!

Connect them all together with a spiderweb of KAS winches so you can control them all simultaneously

[-RanZ-]

necro thread

[HoY]

Didn't even notice. Regardless, it would still be interesting trying with the asteroid mod

[Sirrobert]

Mmmmm what's the DeltaV of a Kerbal jetpack? How many of the green guys would we need to send up there to bring that sucker down? And does one hemisphere of the Mun have enough area for the green guys to stand up there side by side to do the job?

You could theoreticly do it with just 1 RCS thruster (if it wasn't all on rails).

It's simply take longer than our own sun has to live